The present invention relates to apparatus for extracting samples of liquid product from flow lines or tanks.
Certain manufacturing operations require that the immediate or overall composition of a liquid or fluid product flowing through a pipe or contained within a vessel or tank be monitored. Such monitoring ordinarily is accomplished with sampling apparatus, which takes samples of liquid from a main body of the liquid. Where a composite sample of the liquid is required, the sampler may be periodically operated to withdraw a series of small, measured amounts of the liquid as it passes a sampling point. The small, measured amounts are collected and admixed to form a representative sample of the total volume of liquid.
Other uses for samplers are in on-line analysis applications, in which the immediate composition of a liquid must be determined. For this application, the individual samples of liquid are not collected as a composite sample, but instead are received and analyzed separately.
Four exemplary types of sampling apparatus of the type contemplated by the prior art are disclosed in U.S. Pat. Nos. 4,147,062, 4,262,533, 4,475,410 and 4,744,255, issued to Ben E. Jaeger, the present inventor, and the teachings of all of which are incorporated herein by reference. Sampling apparatus of the type disclosed in said patents is attached to an access line or port to a pipe or vessel containing the body of liquid product, so that a liquid sample receiving recess in a plunger of the sampler can be extended through the line and an aperture in the pipe into the body of liquid for receiving a liquid sample in the recess. The plunger is then retracted to deliver the liquid sample to a collection point in the sampler.
The access line usually is attached to the pipe by a flange connected and sealed to the pipe around the aperture therein. The sampler includes, as described in said Jaeger patents, a body having a bore in which a plunger having a sample receiving recess is reciprocated. The bore communicates with the access line. The plunger is reciprocated to a sample receiving position in which the plunger recess is extended out of the body bore and into the pipe to receive a sample of the liquid product contained therein. The plunger is then reciprocated to a sample collecting position in which the plunger recess is retracted back into the bore to deliver the sample to a point in the bore where the sample is removed from the recess and collected.
It can happen that connecting the sampler to the pipe requires use of an access line having a relatively extended length. This can occur, for example, where the pipe is located such that an extended length access line is required in order to position the sampler in a serviceable position. Should the length of the access line be such that upon retraction of the plunger its forward end is positioned in the sampler bore considerably rearward or spaced from the forward outlet from the bore, then whenever and for as long as the plunger is retracted, a considerable length of the forward end of the sampler bore will be exposed to and fill with liquid product from the pipe. This is not a desirable situation, since when the plunger is retracted it is advantageous for the front of the plunger and any part of the sampler bore between it and the forward bore opening to be washed by the flow of product in the pipe. Should a considerable length of bore exist forward of the retracted plunger, the front of the plunger and the bore forward of it may be sufficiently removed from the main body of product so as to be exposed to stagnant product and not be continuously washed by the product. Product may then collect and congeal on the front of the plunger and in the bore forward of it, resulting in contamination of subsequent samples. It can also happen that product can accumulate in and clog the bore forward of the plunger, preventing reciprocation of the plunger and disabling the sampler. This condition is exacerbated by product of a type that is prone to clog when stagnant, such for example as product comprising paper pulp.